The present invention relates to pipe section alignment systems that employ a coherent energy beam and a target positioned to receive the beam, and more particularly to apparatus for releasably and integrally mounting the target to the pipe section being aligned.
The laying of strings of piping sections installing water lines or sewer lines, typically requires coaxial alignment of successive pipe sections. This involves the individual alignment of each pipe section as it is added to the pipe string. A well known and effective system for pipe section alignment includes a laser generating a coherent energy beam, positioned so that the beam is either coincident with or parallel to a longitudinal central axis of the pipe string.
As a pipe section is added to the string, its proximal end is joined to the string, and a transparent target with alignment markings is mounted near its distal end. The laser intersects the target to provide a visual indication of pipe section alignment, to provide a guide for moving the pipe primarily at its distal end to adjust the pipe section toward parallelism with the laser beam.
A variety of these systems are found in the prior art. For example, U.S. Pat. No. 4,968,147 (Shoemaker) discloses a target system including an annular base, an anchoring unit having several extended arms and a square target unit within the annular base. The base has a tapered end that can fit within the bell end of a pipe section, and an opposite flat edge that can abut the spigot end of the pipe section, in which event arms are provided for frictionally engaging the pipe interior. The annular base has holes to receive the corners of the target. Levels on opposite sides of the target facilitate angular adjustment of the base to align vertical and horizontal markings on the target.
U.S. Pat. No. 3,898,743 (Myeress) shows a resilient frame with an upper loop and two lower loops supporting a target, to enable mounting and dismounting of the target within a pipe section, by flexing the frame. The frame flexes to fit different pipe section diameters, in a manner that tends to center the target within the pipe. If desired, laser targets can be set in different positions within pipe sections using adjustable arms or legs, for example as shown in U.S. Pat. No. 4,681,439 (Shoemaker), U.S. Pat. No. 5,095,629 (Klemer et al) and U.S. Pat. No. 3,634,941 (Roodvoets et al).
While the above systems are satisfactory in many respects, they are subject to several disadvantages. Targets with adjustable legs, while accommodating several pipe section sizes, require time and skill to ensure their proper alignment. Typically they are recessed within the piping section and are not conveniently visible, requiring the operator to bend over near the open end of the pipe section to perceive the degree of alignment. Many of the targets are supported merely by gravity, subject to displacement if the pipe section is inadvertently jostled or subject to shock. Thin legs or frames such as those shown in Shoemaker and Myeress are subject to movement from such jostling or impact.
Therefore, it is an object of the present invention to provide a laser alignment target that is quickly and conveniently attached to a pipe section, yet held firmly so that it is not displaced by shock or vibration experienced by the pipe section.
Another object is to provide a means for mounting a laser alignment target as an end cap of a pipe section rather than recessed within the pipe section, to facilitate ease of visually determining pipe section alignment.
A further object is to provide an alignment structure for mounting and maintaining a target with respect to a pipe section, in a manner that continually tends to center the target within the pipe section and functions as a shock absorber between the pipe section and the target.
Yet another object is to provide, in a single device, a laser alignment target and an end cap for providing a substantially fluid tight seal at one end of a piping section.